Synchronizing circuit for electrical commutators



y 1951 c. K. STEDMAN ET AL 2,554,886

SYNCHRONIZING CIRCUIT FOR ELECTRICAL COMMUTATORS Filed June 7, 1947 3Sheets-Sheet 1 I: l8 l6 GE $%Z$ R o PICK UPS 23 flz I cARRIER 2|\GENERATOR MASTER [4 RING 7 COUNTER L MODULATOR 26 ID l l %J J ITRANSMITTER I A0. 24 POWER I 1 I 28 I I l COMMUNICATION LINKS I I i I II I RECEIVER DEMODULATOR 34 I F I 1 FILTER s SEPARATOR 32 I PHASING NET.REGTIFIERS I I TRIGGER LIMITER 4o GENERATOR AMPLIFIER STORAGE RIN ESCAVENGING 42 couNTER CIRCUIT 48 REcoRoERs AGENT y 1951 c. K. STEDMAN ETAL I 2,554,886

SYNCI-IRONIZING CIRCUIT FOR ELECTRICAL COMMUTATORS Filed June 7, 1947 sSheets-Sheet 2 WAVE FORMS IN MASTER SYNC. EQUIP.

TO OTHER TUBES IN MASTER RING COUNTER TO GATHODE 63| OF LAST TUBE J FIG.5

g 94 14\ 82 mllf so T NEG. BIAS PLATE SUPPLY l SUPPLY MODULATED CARRIERTO SLAVE RING INVENTORS CECIL K. STEDMAN A-C CARRIER IISEQET 'M IJI IIERSOURCE SOURCE N BY FIG. 2

AGENT SEARC RGQWI y 29, 1951 c. K. STEDMAN ET AL 2,554,886

SYNCHRONIZING CIRCUIT FOR ELECTRICAL COMMUTATORS Filed'June 7, 1947 3Sheets-Sheet 3 T0 BALANCE TO CATHODE OF RING OF LAST TUBE WAVE FORMS m iT SLAVE SYNC. EQUIP.

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PLATE l NEG. BIAS SUPPLY SUPPLY FILTER $PHASING NETWORK CARRIER IN AGENTPatented May 29, 195i UNITE ATES PATNT OFFICE SYNCHRONIZING CIRCUIT FORELECTRICAL COMMUTATORS Application June '7, 1947, Serial No. 753,296

The present invention relates broadly to electronic commutators and morespecifically to a synchronizing method and means for maintainingsynchronization between a master commutator at a transmitting point anda slave commutator at a receiving point. In most methods of multiplexedtransmissions of intelligence wherein information from severalsub-channels must be transmitted over one common carrier channel it isnecessary to use some form of commutating means to rapidly andsequentially select each of the sub-channels and to transmit theintelligence therein over the common carrier channel, devoting adifierent portion of each cycle to each sub-channel for transmissionpurposes Likewise, at the receiving point slave commutating means mustfunction in synchronism with the transmitting or master commutatingmeans in order to segregate and distribute the original separatesub-channel intelligence signals in the common carrier channel to therespective subchannels in the receiving equipment.

In such a multiplex transmission system some means of insuringsynchronism between the master commutating device at the transmittingpoint and the slave commutating device at the receiving point isnecessary. The present invention is concerned with the synchronizationof slave electronic commutators with a master commutator, each of whichcomprises a plurality of electron discharge devices arrangedelectrically so that the preceding device exercises partial control overthe grid circuit of the succeeding device. Since there is usually someform of feedback from the last electron discharge device in the seriesto the first one in the series to reinitiate the sequence of firing,such a seriesoi electron discharge devices is commonly known as a ringcounter and in the case of thyratrons being used as the electrondischarge devices, a thyratron ring. At the transmitter in such asystem, means are provided which render the electron discharge devicesconductive in succession until the last device of the series is renderedconductive, whereupon the cycle repeats itself. As each electrondischarge device becomes cnductive, its associated sub-channel isautomatically connected through to the common or main carrier channeland at the same time the previous electron discharge device in theseries has been rendered non-conductive, thus disconnecting itscorresponding sub-channel from the main carrier channel. Provision mustbe also made in the transmitter for transmitting an appropriate signalto the receiver to cause the slave com- 6 Claims. (Cl. 177-351) mutatorto function in a similar manner. Obviously, it is necessary that thecycle always begins in corresponding electron discharge devices in boththe transmitter and the receiver, and at the same time. In other words,both phase and time synchronization are necessary.

An object of this invention is to provide means for generating andtransmitting synchronizing signals for maintaining one or more slaverings in synchronism with a master commutator ring.

Another object of this invention is to provide receiving equipment forreception and treatment of synchronizing signals for control of a slavering associated with said receiving equipment.

An additional object of this invention is to provide means for theinitiation of the firing sequence in a slave commutator ring insynchonism with the master ring.

A further object of this invention is to provide means .for phasesynchronization of the slave ring with the master ring once each cycle.

An additional object of this invention is to provide means forreestablishing synchronization automatically after each interruption ofthe synchronizing signals.

Another object of this invention is to provide means for timesynchronization between the master commutating ring and a slavecommutating ring.

A further object of this invention is to provide means for phasesynchronization between a master commutator ring and a slave commutatorring.

The above objects and other features of this invention will becomeapparent to those versed in this art from the following description whenstudied in conjunction with the drawings herein.

Figure 1 is a block diagram showing schematically the relationshipbetween the various components in the transmitter, and receiver units.

Figure 2 is a simplified schematic diagram of the master synchronizingcircuit in the transmitting equipment.

Figure 3 shows the voltage waveforms in the various parts of thetransmitting equipment.

Figure 4 shows a simplified schematic diagram of the slave synchronizingcircuit in the receiving equipment.

Figure 5 shows the voltage waveforms in the various parts of thereceiving equipment.

General description To accomplish phase synchronization, one of theelectron discharge devices in the master ring counter is designated asthe starting point for the beginning of the cycle. Upon being renderedconductive this electron discharge device is caused to transmit a pulseto the receiving equipment. This pulse is necessary to start the cyclein the corresponding electron discharge device at the receiver. At thetransmitter re-cycling of the sequential firing in the master commutatorring goes on continuously. However, in the receiving equipment the slavering commutator can complete only its cycle which has already beenstarted. At the end of its cycle it will become quiescent and wait forthe required pulse from the transmitter before starting a new cycle. Inorder to start, the slave ring counter is entirely dependent upon thespecial pulse from the transmitter. After starting, it can complete itscycle independently of signals from the transmitter, but provision ismade so that it is subservient to a signal continuously received fromthe transmitter, thereby keeping it in step as the cycle progresses frombeginning to end, hence insuring time synchronization. Thus, bytransmitting both continuous and pulse signals, both time and phasesynchronism are assured in the receiver, provided the received signalshave sufficient amplitude to accomplish their intended purpose.

In Figure 1, a diagrammatic block arrangement is shown embodying theessential electronic units and other means comprising this invention.Substantially sinusoidal alternating voltage from source It is dividedand fed into channels l2 and [4. The voltage in channel I2 is fed intothe first trigger generator I6 in which it is modified in waveform,first to a sawtoothed wave and later to sharp pulses of voltage of veryshort-time duration. These short-time voltage pulses are emitted fromthe first trigger generator through channel is and fed into the masterring commutator or counter 28. These short-time pulses of voltage areall of the same polarity and have a frequency of recurrence equal to thefrequency of the voltage source I0. At this point it should be pointedout that the alternating voltage from source I9 is used for timingpurposes only and therefore could be replaced by any one of a largevariety of rhythmically recurrent voltage waveforms, not excludingdirect current pulses. Approximately sine wave voltage is shown in thispreferred embodiment of the invention and is employed in the equipmentpresently in use because of the relative simplicity of generating same.Furthermore, the frequency of the source In may be any small wholenumber multiple of the frequency desired from the sawtooth wavegenerator and still maintain accurate control.

The master ring counter consists of a plurality of electron dischargedevices equal in number to the number of sub-carrier channels which mustshare their time on the common carrier channel. In the particularversion of this invention now in use, the electron discharge devicesconstituting the master ring counter or commutator are of the gas-filledtype commonly known as thyratrons, and for simplicity they shall be sodesignated henceforth in this application. To those versed in the art,it will be obvious that with appropriate circuit modifications the hardtube type of electron discharge device could be used in lieu of thethyratron or gas-filled type tube as cited herein. Likewise, the generaldetails of construction of a ring counter or commutator is well known tothe art and does not concern this invention. As shown in Figure 1, it isthe function of the master ring counter to consecutively andsequentially connect the pickups 23 to the communication carrier channel28 in order that each of the pickups 23 or sub-carrier channels may fora short portion of time have full control of communication carrierchannel 28. Each of the voltage pulses from the first trigger generatorand amplifier it upon arriving at the master ring counter 2e causes thenext succeeding thyratron in the series to ionize and to quench thepreceding thyratron. When the last thyratron in the series ionizes, thefirst one is conditioned to re-cycle automatically, thus, making theprocess continuous. One of the tubes in the master counter is selectedas the starting point for the cycle and its circuits are thereforeadapted to deliver a square wave voltage pulse through channel 26 to themodulator 22. One of these square wave voltage pulses is thus deliveredeach time the starting tube fires, or in other words, once for eachcycle of commutation.

Another portion of the sinusoidal voltage from source I0 is passedthrough channel 54 into the modulator 22. In said modulator thesinusoidal voltage from source i8 and the square wave pulses from themaster ring counter are superimposed or modulated upon the carrierfrequency coming from the carrier generator 2|. After modulation, thecarrier frequency is emitted at 2 with the side-bands of the alternatingvoltage from channel I4 and the square wave pulses from channel 26superimposed upon it.

Although a carrier generator 2| and a modulator 22 has been shown theyare not essential to the basic concept involved in this invention. Forthe particular application in which this invention is now being used itwas necessary to use radio as a communication link, hence, the use ofthe carrier generator and its modulator. To those versed in the art, itwill be obvious that this same method of synchronization could be usedover wire lines as communication link 24. In such an application, thecarrier generator and its modulator could be dispensed with, and thesinusoidal voltage from source I E] and the voltage pulses from channel25 could be transmitted directly over the wires which in such a casewould be communication channel 2 3.

The carrier wave and its side-bands in channel 24 are transmitted to thedemodulator 3% located in the receiving equipment. In this demodulatorthe carrier wave is eliminated and the intelligence in the side-bandsgives the original sinusoidal voltage as found in channel is and thesquare wave voltage pulses similar to those in channel 26. Thiscomposite signal is passed through the separator rectifiers 32 andsegregated into its components. The sinusoidal alternating voltage ispassed into the filter and phasing network 34, and the square wavevoltage pulses are passed into the limiter amplifier 48. After passingthrough the filter and phasing network 34-, the sinusoidal voltage isfed into the second trigger generator 36, thus synchronizing its outputof short-time voltage pulses with the output of the first triggergenerator l6. These short-time voltage pulses in channel 38 are thusheld in synchronism with a similar wave pulse in channel 18 in thetransmitter unit. Although in the transmitter unit the short-timevoltage pulse in channel 18 will fire the tubes in the ring counter insequence, such is not the case at the receiver. To start the sequence offiring in the slave ring counter, it is necessary that the first tube inthe series receive a special form of signal consisting of .one squarewave pulse plus one of the trigger pulses. From the limiter amplifier 40the square wave pulses are passed into the storage and scavengingcircuits 42. After a square wave pulse enters the slave ring counetr 46by means of the channel 64, the first tube is fired by the first triggerpulse received. As a result, the second tube in the sequence in theslave ring counter is so conditioned that the next short-time voltagepulse in channel 38 will fire it and so the series continues to the endof the sequence. Since the filter and phasing network circuits areadapted to introduce an adjustable phase angle, the first tube in theslave ring counter can be caused to fire at the same time as the firsttube in the master ring counter, and from there on the sequence keeps instep by virtue of the time synchronizing effect of the sharp voltagepulses in channels 18 and 38, thus it can be seen that timesynchronization is accomplished by the shorttime pulses in channel 38while the phase synchronization is accomplished by the square wavepulses in channel 44.

If at any time during a cycle of operation of the slave ring counter thesynchronizing signals from the transmitter are interrupted, the triggergenerator in the receiver will be running free as a relaxationoscillator without control and will continue to fire the slave ringcounter tubes to the end of the cycle which has already been started.Therefore to this extent operation of the slave ring counter is notentirely dependent upon receiving signals from the transmitter. However,it is subservient to such signals since the time of firing will becontrolled very accurately by the time synchronizing signal if receivedfrom the transmitter. Upon the completion of its cycle the slave ringcommutator will become quiescent until such time that communicationbetween the transmitter and receiver is re-established and the squarewave voltage pulses are again produced in channel 44 to fire the firsttube in the sequence in the slave ring commutator. If so desired, thetrigger generator in the receiver may be prevented from running free bya slight readjustment of voltages without impairing the over-allperformance of the system.

In Figure 1, for purposes of simplicity two communication links havebeen shown between the transmitting equipment and the receivingequipment. However, with appropriate filters in the receiving equipmentto separate the intelligence from the synchronizing signals, theintelligence in channel 28 may be passed into modulator 22, modulatedupon the carrier frequency from carrier generator 2!, and sent out overchannel 24 to the receiving demodulator 3i]. Appropriate filtersfollowing the demodulator 30 could then remove the intelligence signalscorresponding to those present in the illustrated channel 28 and deliverthem to the slave ring counter for commutation. Such an arrangement isnow actually in use, but such a combination of filters does notconstitute any portion of this invention, hence, for simplicity thesystem is shown with the separate communication links in Fig. 1. anynumber of receivers may be set up with their slave ring counters andrecorders 48 to pick up and record signals for some distant transmitter.

Transmitter circuits In the schematic diagram of the transmitter circuitshown in Figure 2, groups of components corresponding to the block unitsin Figure 1 have been enclosed in dashed lines and assignedcorresponding numbers. The alternating current Obviously source I0 isshown feeding its energy through a transformer into the grid element ofthyratron via conductor 12. The voltages applied to and the componentsassociated with thyratron 50 may be adjusted below the point ofrecurrent relaxation oscillations in which case thyratron 50 would thenbe atrigger tube firing only when it received a positive half wave fromthe alternating voltage source Ill. However, said voltages andcomponents may also be so adjusted that thyratron 50 will functioncontinuously as a relaxation oscillator, the frequency of which isgoverned by the frequency of the alternating voltage from source III. Inthe former case, the thyratron 50 could be regarded as a voltagewaveform converter having a sawtoothed output provided it received animput from the substantially sinusoidal voltage source H]. In the lattercase, thyratron could be regarded as a source sawtooth oscillatory powersynchronized to the frequency of the voltage supply H] by virtue of itsreceiving an input voltage from said supply. Returning now to the actualfunctioning of thyratron 50 and its associated components, the condenser58 is charged with voltage supplied by the plate supply 65, fed throughthe resistor 50. Likewise, as condenser 58 is charged, condenser 62 willalso be charged through resistor 64 since these last two components arein series with each other and in parallel with condenser 58. As thischarging process continues the voltage on the plate element of thethyratron 55 rises to a higher and higher value until the risingsinusoidal voltage applied to the grid element of thyratron 53 makes thegrid sufiiciently positive for the instantaneously prevailing platevoltage to ionize the gas in thyratron 55, thus firing same andcompleting the circuit through to the thyratrons cathode. When thyratron55 fires, it constitutes practically a short circuit across condenser53, thereby discharging the condenser to a voltage too low to sustainthe ionization within thyratron 59, at which time said ionizationextinguishes, thyratron 55 becomes an open circuit once again, and theprocess of recharging condenser 58 repeats itself for another sawtoothcycle. The sinusoidal waveform input to the grid of thyratron 55 and thesynchronized sawtooth waveform output appearing across condenser 58 areboth shown in Figure 3 opposite grid 55 and plate 55, respectively. Itshould be noted that upon firing, thyratron 50 also discharges condenser62 through resistor 54, thus producing a voltage across the grid tocathode circuit of vacuum tube 52. Since condenser 52 was charged with aconsiderable portion of the total plate supply voltage from andsince'the negative terminal of condenser 62 is connected to the gridelement of vacuum tube 52 during the discharge process, vacuum tube 52is blocked momentarily during the discharge of condenser 52. Thismomentary blocking of vacuum tube 52 will cause its plate voltage torise sharply. Consulting Figure 3 again, it will be noted that thesawtooth waveform associated with plate 50 and which appears acrosscondenser 58 is considerably changed by the time it arrives, nowdesignated as grid 52, at the grid element of vacuum tube 52. Thecircuit comprising the condenser 52 and the resistor 64 has an outputwhich is approximately equal to the differential of the input itreceives from condenser 58. Therefore, the sawtooth waveform positivevoltage pulses from condenser 58 are converted to the sharp negativevoltage pulses shown opposite "grid 52 in Figure 3. Because of phaseinversion within the tube 52, these short negative voltage pulses on thegrid of said tube result in positive voltage pulses of the same waveformon the plate of said tube, as shown in Figure 3 opposite plate 52. Sincethyratron 50 is actuated by the steady output of sinusoidal source It,the sharp voltage pulses constituting the output of vacuum tube 52 areaccurately spaced in point of time. Returning now to Figure 2 the twoelectron discharge devices 50 and 52 and their circuits so far discussedconstitute the trigger generator and amplifier I6 enclosed by the dashedline.

The pulse output voltage from the plate of the vacuum tube 52 is fedthrough condenser 68 and conductor l8 into the common grid circuit ofthe master ring counter several stages of which are shown within thedashed line and indicated as 23. The master ring counter within thedashed line 25 consists of a plurality of gaseous discharge devices suchas thyratrons 53, 54, and 55. Although only three thyratrons have beenshown in the master ring counter, for simplicity, any number may be useddepending upon the number of sub-carrier channels which must becommutated and fed into the main carrier channel. The thyratron ringcommutator is a device well known to the art for accomplishingelectronic commutation. However, a brief rsum of its operation will notbe out of place at this point even though the ring commutator does notconstitute a part of this invention.

In the master ring counter the thyratrons 53, 54 and 55 obtain theirgrid bias from the negative bias supply 15. The plates of the thyratronsobtain their power through resistor 12 from the plate supply 65. In thequiescent state when none of the thyratrons 53, 54 and 55 areconducting, all cathodes are virtually at ground potential. By virtue ofthe voltage divider consisting of resistors 35, 82 and I8, and othersimilar voltage dividers in the other counter stages, the control gridswill have some fraction, for example about of the total voltage from thenegative bias supply. The plates of tubes 53, 54, 55, etc., areconnected in parellel and to the common plate supply conductor 14 andcommon plate load resistor 12. Because these tubes are normallynonconductive there will be no voltage drop in resistor I2. Hence, thefull plate supply voltage will be effective at each plate.

Assume now that a sharp voltage pulse arrives on the grid of thyratron53 by way of condensers 68 and 15 from the trigge generator andamplifier 3. The effect is to reduce the bias on the grid of thyratron53 sufficiently to fire the tube. Actually, while this same pulsearrives simultaneously at the grids of all thyratrons and any one ofthem may fire as a matter of chance, for purposes of this description itwill be assumed that thyratron 53 by circuit design or adjustment ismade normally most susceptible of all to firing. Upon ionization orfiring, the oathode of thyratron 53 rises in potential considerablyabove round (see cathode 53 Figure 3). This positive voltage on thecathode appears across resistor 18, therefore it subtracts from thenormally prevailing negative voltage developed by thi resistor in thevoltage divider circuit supplied by the bias supply 75, as described.This reduces the negative bias voltage on the grid of the next thyratron54 and renders this tube more susceptible to firing by voltage pulsefrom the trigger generator and amplifier 16 than any of the otherremaining thyratrons in the master ring counter. During the conductionperiod in thyratron 53 the condenser 84 will be charged to a voltageequal to that across resistance 18. When the condenser 84 is thuscharged, the terminal connected to the cathode of the first thyratron 53is positive and that connected to the cathode of thyratron 54 isnegative. Condenser 84 thereby acts as a D. C. blocking condenser forthe cathode of tube 54 while allowing its grid to follow voltagevariations developed at the cathode of tube 53. With the grid of tube 54positive relative to its cathode, the tube fires on the next positiveimpulse from tube 52. As it does so, the positive voltage developed atits cathode added to the existing voltage on the charged condenser 84results in the application of a high reverse voltage to the thyratron53, extinguishing the latter. The voltage reversing or doubling actiongained by using condenser 84 in this manner is aided in extinguishingtube 53 by the effect of increased load current flowing through resistor72 resulting in a lower available anode potential on tube 53 which is tobe met or overcome by the tubes positive cathode voltage. The cathodepotential may even rise above anode potential in quenching tube 53.Since ionization starts and stops abruptly and the tubes anode currentis relatively constant during conduction, the cathode voltage, relativeto ground, is a square wave as shown opposite cathode 53 in Figure 3.Upon establishing conduction in thyratron 54 condenser is charged as wascondenser 84 and the control grid bias on tube 55 is reduced as it wasin the case of thyratron 54, and in this manner the process justdescribed repeats itself in each stage to the last tube (not shown) inthe series, whereupon the over-all cycle is repeated since the last tubein the series preconditions the first thyratron 53 by reducing its gridbias. It should be noted that one terminal of condenser 94 is indicatedas being connected to the cathode of the last tube in the series. At theending of the over-all cycle when thyratron 53, or the first tube inthis series, is again fired, a pulse thereby generated and appliedthrough condenser 34 will quench the last tube in the series.

The three conductors 38, 33 and 92 brought out from the cathodes of thethyratrons 53, 54 and 55, respectively, are the conductors used forcontrolling the circuits or other devices which must be operated insequence. Another method sometimes used is to place a relay between thecathode and ground in the cathode circuit of each thyratron.

The carrier source 2| is the source of energy used as a carrier fortransmission of the time and phase synchronizing pulses and may also beused to transmit the intelligence from each one of the sub-channels. Thecarrier frequency may be either radio or supersonic. For the particularexample of the invention shown in Figure 2, the circuit components shownenclosed in the dashed line 22 constitute the modulator. The electrondischarge device 55 is a vacuum tube diode-triode adapted to have therequired non-linear characteristics suitable for modulation.Substantially sinusoidal alternating voltage from source In is fed alongconductor 54 through resistor [5, condenser ll and into the grid circuitof the electron discharge device 55. Additional alternating voltage isfed into the grid of tube 56 from the carrier source 2! throughtransformer 69. The resultant is the sum of the two voltages, fromsource It! and the carrier source 2|, applied to the grid of tube 56.The approximate waveform at this point of the circuit is shown in Figure3, section 51 of the waveform shown opposite grid 56. By virtue of tube56 being adjusted for modulation, the waveform on the grid as shown inFigure 3 resultsin a waveform appearing on the plate of tube50 as shownin Figure 3, section 59 shown for plate 56. Such a modulated wave couldnow be transmitted to the receiver and it would contain enoughintelligence to keep the thyratrons in the slave ring counter firing intime with the thyratrons in the master ring counter, however, therewould be no means to determine or to maintain the desired phase relationbetween the two rings. In other words, if the sequence of firing in thereceiver or slave ring counter dropped one step behind the master ringcounter or if it gained one step, there would be no means for correctingthis condition. Therefore, it is necessary to transmit an additionalsynchronizing pulse of voltage in order to accomplish phasesynchronization.

Returning again to thyratron 53, the first in the series in the masterring counter, it will be noted that a conductor 26 is connected directlyto the cathode element of said tube. When thyratron 53 is renderedconducting, as mentioned before, the cathode rises to an appreciablyhigh positive voltage very rapidly (see cathode 53 waveform in Figure3). This results in a voltage pulse being transmitted along conductor 26through resistor 21, condenser 20 and to the diode plate of vacuum tube56. As a result of this positive voltage on the diode plate a currentfiows between the plate and the cathode of vacuum tube 56, thus causingthe cathode to also rise to a higher positive voltage during the pulseperiod (see cathode 5B Figure 3). Since a rise in positive voltage onthe cathode corresponds to-a rise in negative voltage on the grid, thewaveform on the grid of vacuum tube 50 will appearat this time similartosection 6I in the Waveform shown for grid 56 in Figure 3. Due to themodulation characteristics of vacuum tube 56 this waveform shown on grid56 will appear in the plate circuit as shown in section 03 of'thewaveform for plate 56 in Figure 3. Such a waveform now contains theoriginal sine wave and the phase synchronizing pulse in its side bandsand said modulated wave passes through the transformer 01 and outthrough conductor 20. It may then be directly radiated or passed throughsufficient amplifying means to increase its power before being radiatedto the receiving station. It should be noted at this point that thepulse transmitted to the modulator from thyratron 53 occurs only whenthyratron 53 is ionized; in other words, once for each cycle ofoperation of the thyratron ring. With slight modifications obvious tothose versed in the art and without departing from the spirit and scopeof this specification, the phase synchronizing pulse may be applied tothe modulator in the opposite polarity thereby causing an increase incarrier amplitude rather than a decrease. However, the final radiofrequency amplifier could not then operate as efficiently as with thearrangement shown, since it would be called upon to function at peakpower only during a phase synchronization pulse and at other times onlyat partial capacity. The circuit herein shown enables the radiotransmitter to function normally at peak power. If, however, frequencymodulation were used instead of amplitude modulation as in the presentequipment,

Receiver circuits In Figure 4, the various components shown enclosed indashed lines correspond to similarly numbered block units shown inFigure 1. The modulated carrier as received or after being amplified isfed in through transformer I02 to the demodulator 30 which consists of adiode vacuum tube detector I04 and its load resistor I06 and filtercondenser I08. The modulator carrier has the waveform shown at the inputto I04 in Figure 5. The diode rectifier I04 demodulates the receivedsignal and delivers to its load resistor I06 a voltage having a waveformsimilar to that shown in Figure 5 for the output of I04, which consistsof a small amplitude sine wave with periodic larger amplitude negativepulses. At this point there may still be some carrier present.Therefore, the signal is then passed through the resistance andcondenser filter consisting of the condenser H0 and the resistance I09.The voltage appearing across condenser H0 is then fed through condenserII2 into the separator rectifier unit 32 consisting of the diodes H4 andIIS and their associated components. It should be noted at this pointthat the plate of diode I I4 is connected to the cathode of diode H0.The local circuit of the diode H0 beginning at its plate, which is alsoconnected to the condenser II2, includes the reactor H8. the batteryI20, the resistor I22 and the cathode of the same diode H4. The cathodeof said diode H4 is also the output terminal and its voltage isdelivered through condenser I30 to the filter and phasing network 34.The local circuit of diode II6 starting at its plate element includesthe resistance I20, the battery I26, the reactor H8 and the cathode ofthe same diode H6. The output of the diode H0 is taken from its platethrough lead I28. The bias batteries I20 and I26 are each connected inseries with their respective diodes with the positive terminal of thebattery I20 connected to the plate element of the diode H4, and thenegative terminal of the battery I26 connected to the plate element ofdiode H0. The battery I 20 in series with diode Il4 has its voltageadjusted to be equal to or slightly greater than the peak value of thesinusoidal voltage supplied to the diode H4 from the rectifier circuitincluding the diode I04. The bias voltage from battery I20 has alimiting function in that with its value adjusted as described thesinusoidal component in the input to diode I I4 corresponding to thesinusoidal voltage from the A. C. source I0 in the transmitter can passthrough said diode II4 without change and on through the condenser I 30to the filter and phasing network 34. However, because of the output ofdiode I04 coming from its cathode the phase synchronizing pulses fromthe transmitter are delivered to the plates of diode II as strongnegative voltage pulses. Since the negative half cycles ofthe-sinusoidal components are practically equal to the voltage ofbattery I 20, cutoff in the diode IIt is approached but not exceeded bythe sinusoidal voltage. However, when the strong phase synchronizingnegative pulses apforms.

pear at the plate of diode H4 complete cutofi is effected. Hence, thesepulses are canceled out by this procedure. Actually the output of diodeII4 will not be perfectly sinusoidal for all wave- This characteristicis shown in a fiat portion of the waveform in Figure 5, show as theoutput of H4, and in time phase with the large amplitude negative pulsesin the waveform of the output of I04, same figure.

By reverse process, due to the fact that diode H6 is connected inreverse with respect to diode H4 and battery I26 biases diode H6 beyondcutoff for all signals except strong negative pulses of voltage, thesinusoidal component of the demodulated wave is eliminated in thiscircuit and only the phase synchronizing pulse component is passedthrough, being substantially unchanged, as shown in Figure for theoutput of H6. These pulses of negative voltage are fed through conductorI28 into the limiter amplifier 46 to the grid of vacuum tube I32. Anegative pulse on the grid of vacuum tube I32 results in a rise involtage on the plate of said tube (see output of I32 in Figure 5). Theresulting positive pulse passes through condenser I33, through diode I34and out of the limiter amplifier circuit 40 to the storage andscavenging circuit 42 to charge the storage condenser I36 (see voltageacross I36}? Figure 5). Because of the, valve action of diode I34, thepositive pulse from the plate of tube I32 after charging condenser I36cannot leak back and be drained off by resistor I31. As shown in sectionIE5 of the output of II 4 in Figure 5, the phasing pulse from diode II6occurs one-half cycle ahead of the peak of the timing wave, therefore itis necessary that condenser I36 store said phasing pulse until thetiming wave arrives because it is the sum of the phasing pulse and thetiming wave which is necessary to control the firing of the firstthyratron in the slave ring 46. The grid to ground circuit of thyratron43 consists of resistance 4i, conductor 44, resistance I35 andresistance I 38. Since the terminal of condenser I36 connected to thegrid end of resistance 535 is positive, the net result is a reduction ofthe quiescent negative voltage on the grid of thyratron 43 whencondenser I36 becomes charged through diode I34. The resulting voltageon condenser I36 produces a reduced bias on the control grid ofthyratron 43 which preconditions this tube to be susceptible to firingby the next pulse from the trigger generator and amplifier 36. Uponignition or ionization of thyratron 43 the counting or commutating cyclein the receiver will have been started and there is no further need forthe charge. stored in condenser I36. vThere-- fore, to accomplish theremoval of such charge in condenser I36 a lead I41 connected directly tothe cathode of thyratron 43 feeds a voltage pulse through resistance I42to the grid of the vacuum tube I44. Since the cathode of thyratron 43 ispositive with respect to ground, this puts a positive voltage on thegrid of triode I44, thus, causing the plate to cathode circuit of saidtriode to discharge the stored voltage in condenser I36 with the firingof the thyratron 43.

The trigger generator and amplifier enclosed by dashed line 36 need notbe discussed in detail here since it is preferably identical with thecorresponding circuits in the transmitting station.

As cited before, the trigger generator has an output connection to theslave commutator ring 46 through condenser 38 which delivers timesynchronizing pulses to the ring counter and con:

tinues to do so even though reception from the transmitter ismomentarily interrupted during a cycle of operation. Hence, after thecycle has once been started, the trigger generator can continue to firethe thyratrons in the slave ring 46 to the end of said cycle. As in thecase of the transmitter trigger generator, the receiver triggergenerator is also subservient to an alternating voltage input derivedfrom the filter and phasing network which has an output waveformsubstantially corresponding to that of the alternating current powersource at the transmitter. The filter and phasing network 34 isnecessary to improve the waveform of the output of diode H4 and toprovide some phase control of the time synchronizing voltage pulseoutput of the trigger generator and amplifier 36. Such control isnecessary in order that firing of corresponding tubes in the master ringcounter and the slave ring counter can be initiated and terminatedsimultaneously in both rings.

The design and operation of the slave ring commutator in the receivingcircuits is practically identical to those same circuits in thetransmitter. Therefore, they need not be discussed here in detail.However, one difference does exist and that consists of omitting, in theslave ring, the direct current connection between the cathode of thelast thyratron in the sequence and the grid circuit of the firstthyratron 43 in the sequence. This omission prevents preconditioning ofthe grid of thyratron 43 when the last thyratron fires and therebyprevents automatic re-cycling of the slave ring counter, each cyclebeing initiated only when a phase synchronizing pulse signal has beenreceived and stored in condenser 136. It is, however, necessary toprovide the capacitor I56 connected between the cathodes of the firstand last tubes in the sequence in order to quench the last tube upon thefiring of the first one. It will therefore appear that the commutationcycle once started by the ionization of tube 43 will continue through tothe end of the sequence but will stop there and not repeat with firingof tube 43 until reception of the required phase synchronizing pulse anda coincidental timing pulse from tube 36. In this manner, phasesynchronization is reestablished at the beginning of each commutationcycle of the slave ring. As in the case of the master commutating ring,the slave ring has leads I46 and I43 in Figure 4) brought out from thethyratron cathodes for controlling the devices or circuits which must beoperated in the proper sequence; or in lieu of the above, a relay may beplaced in each thyratron cathode lead as previously described.

The above is a preferred embodiment of this invention, and to thoseversed in the art many variations of same will be immediately suggestedby the disclosures herein. Therefore, we (101106 intend to be limited tothe specific circuits, components or methods disclosed in the drawingsor specification of this application.

We claim:

1. In a telemetric system, a continuouslyoperable transmitting circuithaving a plurality of elements operable successively in recurring cyclesto select individual transmitting sub-channels for intelligencetransmission, a receiving circuit counter having a plurality ofelements, including a starting element and corresponding to saidtransmitting circuit elements, and associated means to operate themsuccessively through a single complete counter cycle to selectivelyenersize individual receiver sub-channels corresponding to saidtransmitting sub-channels, means operable to transmit and receive a timesynchronizing wave synchronized with the successive operation of theelements in the transmitting circuit, and further operable to controlsaid associated means to synchronize the receiving circuit counterelements with the transmitting circuit counter elements during eachcycle of operation thereof, and means operable in response to each fullcycle of operation of said transmitting circuit to transmit and receivea phase synchronizing impulse therewith for application to saidreceiving circuit counter starting element to initiate operation of saidcounter in recurring cycles synchronously with said transmittingcircuit, thereb to selectively energize said receiver sub-channelssynchronously with their corresponding transmitting sub-channels fortransfer of intelligence over such sub-channels intermittently.

2. In a telemetric system, a continuously operable transmitting circuithaving a plurality of elements operable successively in recurring cyclesto select individual transmitting sub-channels for intelligencetransmission, receivin circuit counter means having a plurality ofcounter elements, including a starting element, correspondin to saidtransmitting circuit counter elements and inherently operablesuccessively through a single complete cycle of the counter toselectivel energize individual receiver sub-channels corresponding tosaid transmitting sub-channels, means operable to transmit and receive atime synchronizing wave synchronized with the successive operation ofthe elements in the transmitting circuit, and further operable tosynchronize the receiving circuit counter elements therewith during eachcycle of operation thereof, and means operable in response to each fullcycle of operation of said transmitting circuit to transmit and receivea phase synchronizin impulse therewith for application to said receivingcircuit counter starting element, the dura of such synchronizin impulsesubstarfiifally e ce'difig'and overlapping, in point of time, asynchronizing peak of said time synchronizing wave, and the magnitude ofsuch synchronizing impulse being such that neither of said impulse norsynchronizing peak alone is sufficient to initiate a cycle of operationof said counter, but the resultant of both is adapted so to initiatesuch operation, whereby said counter is initiated in recurring cycles ofoperation synchronously with said transmitting circuit, thereby toselectively energize said receiver sub-channels synchronously with theircorresponding transmitting sub-channels for transfer of intelligenceover such sub-channels intermittently.

3. In a telemetric system, a transmitting circuit counter having aplurality of elements operable to select individual sub-channelssuccessively for intelligence transmission, first wave generating meansactuating said counter through recurring cycles of operation of itselements in succession, a receiving circuit including a normally freerunning wave generating means having means for establishing its normalfrequency substantially at that of said first Wave generatin means andalso having synchronizing control means therefor responsive to a timesynchronizing wave to override said frequency establishing means, areceiving circuit counter having starting control means and having aplurality of elements controlled by said normally free running wavegenerating means for successive operation corresponding to the sequenceof said transmitting circuit counter after such receiving circuitcounter is started, such elements in turn controlling energization ofreceiver sub-channels corresponding to transmitter sub-channels,time-synchronizing means transmittin and receiving a wave synchronizedwith said transmittin circuit Wave generating means for application tosaid synchronizing control means of the receiving circuit wavegenerating means to synchronize operation thereof, hence of saidreceiving circuit counter, with said transmitting circuit wavegenerating means and counter, for energizing receiver sub-channels inprecise synchronization with corresponding transmitter sub-channels, andphase-synchronizing means transmitting and receiving a synchronizingimpulse once each cycle of operation of said transmitting circuitcounter for application operatively to said starting control means, toinitiate cyclic operation of said receiving circuit counter in phasesynchronization therewith, whereupon the receiving circuit counter,after each start, runs through the ensuing cycle of operation of itselements under control of said normally free running wave generatingmeans at times when the time synchronizin wave is received and appliedthereto and also at times when it is for any reason interrupted.

4. The telemetric system defined in claim 3, wherein the means fortransmitting and receiving the generated wave and the phasesynchronizing impulses operate in a single transmission carrier channel,and include means at the transmitter to mix the time synchronizing waveand the phase synchronizing impulses for application to the carrier,means at the receiver to separate such wave and impulses, suchseparating means comprising a biased detector insensitive to theseparated wave but operatively connected to the starting control meansto deliver the separated impulses thereto, and an amplitude limitingdetector responsive to the separated time synchronizing wave butinsensitive to the separated impulses, and connected to thesynchronizing control means.

5. The telemetric system defined in claim 4, wherein the startingcontrol means is responsive selectively to the combination of aseparated impulse and a concurring cycle of the separated timesynchronizing wave, said system further comprising means applying theoutput of the amplitude limiting detector to the counter startingcontrol means, storage means responsive to the biased detector to storeand thereby prolong the separated phase synchronizing impulse producedthereby for application to the starting control means in timecoincidence with a cycle of such detector output, and means connected tothe receiver counter and operable to discharge such storage meansautomatically in response to each cycle of operation of such counter.

6. The telemetric system defined in claim 3, wherein the receivingcircuit counter elements comprise thyratron switch tubes, cathode loadresistors therefor, direct-current connecting means interconnecting thecathode of each tube with the control grid of the succeeding tubecascade fashion, and direct-current blocking condensers interconnectingthe cathode of each tube with that of the tube succeeding it, means toapply anode voltage to said tubes through a common plate load resistor,means interconnecting the receiving circuit wave generating means andthe control elements of each of said tubes, and. means, including thestarting control means, in-

15 16 terconnecting the control element of only one of said tubes withthe means receiving the phase UNITED STATES PATENTS synchronizingimpulses. Number Name Date CECIL STEDMAN' 1,914,407 Demarest June 20,1933 HARRY PRICE 5 2,048,081 Riggs July 21, 1936 ROBERT WISNER-2,055,309 Ramsey Sept. 22, 1936 2,076,335 Dallenbach Apr. 6, 1937REFERENCES CITED 2,381,920 Miller Aug, 14, 1945 The following referencesare of record in the 2,400,574 Rea et a1 May 21, 1946 file of thispatent: 10

